Successful Therapy of Murine Visceral Leishmaniasis with Astrakurkurone, a Triterpene Isolated from the Mushroom Astraeus hygrometricus, Involves the Induction of Protective Cell-Mediated Immunity and TLR9

Abstract

eIn our previous report, we showed that astrakurkurone, a triterpene isolated from the Indian mushroom Astraeus hygrometricus (Pers.) Morgan, induced reactive oxygen species, leading to apoptosis in Leishmania donovani promastigotes, and also was effective in inhibiting intracellular amastigotes at the 50% inhibitory concentration of 2.5 g/ml. The aim of the present study is to characterize the associated immunomodulatory potentials and cellular activation provided by astrakurkurone, leading to effective antileishmanial activity in vitro and in vivo. Astrakurkurone-mediated antileishmanial activity was evaluated by real-time PCR and flow cytometry. The involvement of Toll-like receptor 9 (TLR9) was studied by in vitro assay in the presence of a TLR9 agonist and antagonist and by in silico modeling of a three-dimensional structure of the ectodomain of TLR9 and its interaction with astrakurkurone. Astrakurkurone caused a significant increase in TLR9 expression of L. donovani-infected macrophages along with the activation of proinflammatory responses. The involvement of TLR9 in astrakurkurone-mediated amastigote killing has been evidenced from the fact that a TLR9 agonist (CpG, ODN 1826) in combination with astrakurkurone enhanced the amastigote killing, while a TLR9 antagonist (bafilomycin A1) alone or in combination with astrakurkurone curbed the amastigote killing, which could be further justified by in silico evidence of docking between mouse TLR9 and astrakurkurone. Astrakurkurone was found to reduce the parasite burden in vivo by inducing protective cytokines, gamma interferon and interleukin 17. Moreover, astrakurkurone was nontoxic toward peripheral blood mononuclear cells of immunocompromised patients with visceral leishmaniasis. Astrakurkurone, a nontoxic antileishmanial, enhances the immune efficiency of host cells, leading to parasite clearance in vitro and in vivo.

Therapeutic effect of ursolic acid in experimental visceral leishmaniasis

“…Additionally, an oleanane triterpenoid derivative (maesabalide III) isolated from Maesa balansae showed in vivo activity against L. donovani following administration of a single subcutaneous dose on either day 1 (prophylactic treatment) or day 28 (curative treatment) after infection (Maes et al., 2004). These data suggest that in addition to their therapeutic effects, some terpenes can also exert modulatory immune effects on animals (Yamamoto et al., 2014, Mallick et al., 2016). …”

Cytokines: Key Determinants of Resistance or Disease Progression in Visceral Leishmaniasis: Opportunities for Novel Diagnostics and Immunotherapy

“…Mucosal disease caused by L. (V.) braziliensis is also associated with elevated levels of IL-17 response (167). Treating VL using curdlan, a b-glucan immunomodulatory molecule induces Th1 cytokines with IL-12, IL-22 and IL-23 (273), while another immunomodulator Astrakurkurone is effective against experimental VL by inducing IL-17 along with IFN-γ (274). While these reports are suggestive of a protective role of IL-17 in VL, other reports suggested the involvement of IL-17 in exacerbating experimental VL in murine model (275) raising questions about its precise role in VL pathogenesis.…”

Live Attenuated Leishmania donovani Centrin Gene–Deleted Parasites Induce IL-23–Dependent IL-17–Protective Immune Response against Visceral Leishmaniasis in a Murine Model

“…Likewise in case of Leishmania infection, several studies have demonstrated that, apart from Th1 cytokines, IL-17 plays a crucial role in host protection against both human and canine VL caused by L. donovani and L infantum respectively (21, 22). Successful therapy of VL with different immune modulatory molecules has been shown to induce Th1 cytokines, along with IL-17, IL-22, and IL-23 (23–25). A recent report demonstrated that leishmanial Ag-stimulated DCs exhibit a potent anti-leishmanial role by the induction of proinflammatory cytokines and generation of Th17 cells during experimental VL infection (26).…”